Aromatic carbonate resins are well known thermoplastic resins which, due to their many excellent mechanical properties, are used as thermoplastic engineering materials. The aromatic carbonate resins exhibit, for example, optical clarity, good thermal stability, good impact properties, and toughness. These resins are utilized as films, sheet articles, and molded articles.
However, the aromatic carbonate resins are somewhat susceptible to surface scratching and abrasion, attack by many common solvents, and to degradation by ultraviolet radiation. The problems of relatively low scratch and abrasion resistance and susceptibility to attack by chemical solvents have been addressed by providing various surface coatings on aromatic carbonate resin articles which coatings serve to protect the underlying substrate from scratching and attack by chemical solvents. Among the various coatings used to protect the aromatic carbonate resin articles are the acrylics. Some of these acrylic coatings are described in U.S. Pat. Nos. 3,968,305, 3,968,309, and 3,582,398.
Certain acrylic coatings have been found to be particularly advantageous when applied onto aromatic carbonate resin articles. These coatings may generally be characterized as the ultraviolet radiation cured, i.e., photocured, acrylic coatings. U.S. Pat. No. 4,198,465 describes a polycarbonate article having on its surface a UV cured acrylic coating comprised of the photoreaction products of (i) at least one polyfunctional acrylate monomer having from 2 to about 4 functional groups attached to an aliphatic hydrocarbon residue containing 1-20 carbon atoms and optionally having ether linkages and/or hydroxyl groups, (ii) a photoinitiator, and (iii) resorcinol monobenzoate; U.S. Pat. No. 4,384,026 describes an aromatic carbonate resin article having on its surface an ultraviolet radiation cured coating comprised of the photoreaction products of polyfunctional acrylate monomers and acrylic modified polymers; and U.S. Pat. No. 4,477,529 describes a plastic article having adhered thereto a translucent and decorative ultraviolet radiation cured coating which is wrinkled in a macroscopically irregular but microscopically regular manner and comprised of the photoreaction products of (i) at least one polyfunctional acrylate monomer, (ii) certain polysiloxane-polyether block copolymer surfactants, and (iii) azobisisobutyronitrile.
In order to protect the underlying aromatic carbonate resin substrate from degradation by ultraviolet radiation the acrylic coatings may contain ultraviolet radiation absorbers or stabilizers. These ultraviolet radiation absorbers may be latent ultraviolet radiation absorbers such as, for example, resorcinol monobenzoate described in the aforediscussed U.S. Pat. Nos. 4,198,465 and 4,477,529, or active ultraviolet radiation absorbers such as those described in aforediscussed U.S. Pat. No. 4,384,026. The incorporation of ultraviolet radiation absorbers, particularly the active absorbers, into photocurable acrylic coating compositions, however, presents somewhat of a problem since these coating compositions must also contain a photoinitiator or photosensitizer in order to effect the cure of the polyfunctional acrylate monomers. Generally, the presence of the active ultraviolet radiation absorbers in the photocurable coating compositions results in an incomplete cure of the coating composition. This is due to the fact that these active absorbers absorb ultraviolet radiation thereby reducing the amount of said radiation available to activate the photoinitiators. This reduces the effectiveness of the photoinitiators thereby resulting in an incomplete cure of the polyfunctional acrylate monomers. The incomplete cure of the coating composition results in a coating having reduced weathering resistance as compared with a completely cured coating.
While this problem of incomplete cure is generally not significant with the use of latent ultraviolet radiation absorbers such as resorcinol monobenzoate, these latent absorbers are generally not quite as effective as the active absorbers. Thus, while the coatings containing these latent absorbers are quite useful for most applications there nevertheless exist certain applications where coatings exhibiting better protection against ultraviolet radiation are required.
It is, therefore, an object of the instant invention to provide aromatic carbonate resin articles having on their surface a photocured acrylic coating containing an active ultraviolet radiation absorber wherein said coatings are substantially completely cured and exhibit improved weatherability.